1. Field of the Invention
The present invention relates to a graft copolymer and a process for producing the same. More particularly, it pertains to a process for efficiently producing a styrenic graft copolymer having excellent impact resistance and heat resistance and favorable compatibility with other types of resins by graft copolymerizing an ethylenically unsaturated monomer onto a styrenic copolymer, especially onto a styrenic copolymer having a syndiotactic configuration; a novel styrenic graft copolymer; a resin composition containing the graft copolymer; and a multi-layer material containing the graft copolymer layer.
2. Description of the Related Arts
Heretofore, styrenic polymers produced by the radical polymerization method have been molded to various shapes by various molding methods and widely used as domestic electrical appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers and other industrial materials. Because of their atactic configuration in stereochemical structure, however, such styrene polymers have suffered the disadvantages of inferior heat resistance and chemical resistance.
In order to solve the above-mentioned disadvantages of the styrenic polymers having atactic configuration, the group of the present inventors succeeded in the development of the styrene polymers having a high degree of syndiotactic configuration, and further the styrenic copolymers of a styrene monomer and other comonomer (refer to Japanese Patent Application Laid-Open Nos. 104818/1987, 187708/1987 and 241009/1988).
These developed styrenic polymers are excellent in heat resistance, chemical resistance and electrical properties and are expected to find application use in a variety of fields.
Nevertheless, the above developed polymers, especially syndiotactic polystyrene still involve such problems as poor compatibility with other types of resins, little adhesion to a metal, etc. and insufficient impact resistance.
Meanwhile, the polymerization of an olefinic monomer by a cationic transition metal complex has been reported since many years ago. For example, (1) Natta et. al reported the polymerization of ethylene using the composition of titanocene dichloride and triethylaluminum as the catalyst (J. Polymer Sci., 26, 120 (1964)). Breslow et. al reported the polymerization of ethylene by the use of titanocene dichloride and dimethylaluminum chloride as the catalyst (J. Chem. Soc, 79, 5072 (1957)). Further, Dyachkovskii et. al suggested that the polymerization activity of ethylene by the use of titanocene dichloride and dimethylaluminum chloride as the catalyst is based on monomethyl titanocene cations (J. Polymer Sci., 16, 2333 (1967)). However, the activity of ethylene according to the above-mentioned methods is extremely low.
In addition, (2) Jordan et. al reported the synthesis of biscyclopentadienylzirconium methyl(tetrahydrofuran) tetraphenyl borate by the reaction of dimethyl zirconocene with silver tetraphenylborate, isolation of the reaction product and the polymerization of ethylene by the use thereof (J. Am, Chem. Soc, 108, 7410 (1986)), and also the synthesis of biscyclopentadienylzirconium benzyl(tetrahydrofuran) tetraphenylborate by the reaction of benzyl zirconocene with ferrocenium tetraphenylborate and isolation of the reaction product (J. Am. Chem. Soc. 109, 4111 (1987)). It was confirmed that ethylene was slightly polymerized by the aforestated catalyst, but the polymerization activity was extremely low.
Moreover, (3) Turner et. al proposed a method for polymerizing .alpha.-olefin by the use of the combination of a boron complex containing a specific amine such as triethylammonium tetraphenylborate, triethylammonium tetratolylborate, triethylammonium tetra(pentafluorophenyl) borate and a metallocene as the catalyst (refer to Japanese Patent Application through PCT Laid-Open No. 502036/1989). However, the aforestated catalyst systems (1) through (3) are applicable only to the restricted polymerization, that is, homopolymerization of an .alpha.-olefin and copolymerization of .alpha.-olefinic comonomers and at the present time, are not actually evolved to the polymerization of a styrenic monomer.
Meanwhile, Japanese Patent Application Laid-Open No. 7705/1991 discloses a copolymer of an olefin and syndiotactic polystyrene and a copolymer of an olefin, an unsaturated carboxylic acid ester and syndiotactic polystyrene. The copolymers thus obtained are high in crystallinity when the content of a comonomer is low, but become amorphous as the content of a comonomer increases, thus making it impossible to fully realize the mechanical, thermal and chemical properties of syndiotactic polystyrene of its own.
Accordingly, the above-mentioned copolymers suffer the drawback that they can not produce a wide variety of materials which make use of the characteristics of syndiotactic polystyrene by compounding with other thermoplastic resin or filler because of the restriction to the amount of a comonomer to be copolymerized.
The use of a third component, that is, a compatibilizing agent for the resin is taken into consideration but is not favorable, since a suitable compatibilizing agent is not found because of the higher molding temperature of syndiotactic polystyrene and further, the addition of such an agent possibly causes the degradation in the performance of the composition obtained.
Attempts have been made from the different point of view to contrive the evolution of a wide range of application of syndiotactic polystyrene by forming a laminate of it and one of a variety of materials, particularly resinous materials and metals to make use of the characteristics of each of the materials to be used. As an example, syndiotactic polystyrene may be multi-layered, but the lack of interfacial adhesion between the layers causes interlaminar peeling or delamination, making the laminate practically unusable. Although the above-mentioned copolymer is excellent in terms of interfacial adhesion, they are rendered amorphous with increase in the content of a comonomer, thereby markedly degrading the performance thereof. Consequently, a laminating material with excellent properties can not be produced from such copolymers.
Under such circumstances, intensive research and investigation were continued by the present inventors in order to overcome the disadvantage of the aforesaid syndiotactic polystyrene and at the same time, develop a styrenic copolymer excellent not only in compatibility with other types of resins and adhesion with metals but also in impact resistance.
In the course of the research, it has been found that a specific styrenic copolymer onto which an ethylenically unsaturated monomer is graft polymerized possesses the characteristics meeting the foregoing object. Further research continued by the present inventors finally led to success in developing a process for producing at a high productivity a styrenic copolymer having surpassing properties at an optional graft ratio and at a high productivity by efficiently proceeding with the graft copolymerization. In addition, it has been discovered that the graft copolymer obtained by the above developed process is effective for a variety of applications.